Prize-winning Atlantic Online cartoonist Sage Stossel created her Find-the Animals bestseller On the Loose in Boston in 2009, in which animals from Franklin Park Zoo escape and show up in settings from Fenway Park to Faneuil Hall. She followed it with On the Loose in Washington, D.C. in 2013, when the National Zoo's animals got the same idea, and cavorted around our nation's capital from the White House to Capitol Hill. Next stop? The San Diego Children...